In a stand mixer, combine the flour, sugar, salt, and crumbled fresh yeast. Mix briefly, then gradually add the beaten eggs, kneading until smooth, about 2-3 minutes.
Gradually incorporate the softened butter, kneading for up to 20 minutes for that perfect texture.
Cover the dough with a clean kitchen towel and let it rise in a warm place until it doubles in size, which should take about 2 hours.
In a saucepan, heat milk and butter together, infusing with the vanilla pod.
In a separate bowl, whisk the egg yolks, sugar, cornstarch, and a bit of flour. Merge the mixtures and cook over low heat until thickened, then chill.
Roll out the risen dough and spread the chilled custard over half. Sprinkle with mini chocolate chips and fold over the other half.
Cut into 8 rectangles, place on a baking sheet, and let rise again for about 2 hours.
Preheat your oven to 350°F (180°C). Brush the tops with egg wash and bake for 10-12 minutes, or until they are golden brown and fragrant.
Once baked, brush the hot brioches with sugar syrup for a lovely shine. Optionally, dust with powdered sugar to add a sweet finishing touch.